Shame your neighbours are giving you so much pressure you have no time. Anyone who trains dogs will tell you there are no quick fixes. So, first thing I would recommend, is before you leave your lovely Lab, a very long exhausting off lead walk. A swim if you have a river close by. A weary dog is less likely to be so fretful. Then freeze a large Kong with mackerel in tomato sauce, or cream cheese, or such like. You can also purchase toys that use their mind (look online). Don't give these items at other times to devalue them. Give when you leave the house so these things are seen as such a wonderful treat, you going out is a very good thing! Build up the time left alone gradually. And a bottle of wine, bunch of flowers, chocolates to the neighbours, with an explanation (or a letter if they're a bit hostile) to say you are trying your absolute best to sort it out and he is, after all, only 5 months old! A mere baby. A safe den is a good idea, crate or otherwise. And no reassurance nonsense upon leaving. Just go without a lot of fuss. Good luck and best wishes, Gill